The invention relates to a method for controlling the power supply system of at least two power loads, in particular a power load and a firing device of a vehicle occupant protection system. The invention also relates to an emergency power supply system for a vehicle occupant protection system.
Modern vehicle occupant protection systems generally operate in such a way that one or more control units are connected to sensors that detect states that are dangerous for the vehicle occupants and trigger vehicle occupant protection devices such as airbags, seatbelt pretensioners, and other such devices in accordance with predetermined algorithms. The vehicle occupant protection devices are frequently triggered by firing devices that have an electrically fired firing cap whose firing leads to the explosive generation of propellant gas with which an airbag is inflated, a seatbelt pretensioning device tensioned, etc.
In the case of an accident, the vehicle battery can be disconnected from the vehicle occupant protection system so that an emergency power supply has to be ensured at least for a specific time period after an impact. This time period is generally referred to as the autarchy time period. In the case of a head-on impact or side impact this autarchy time period is, for example, 125 msec.
Recent vehicle occupant protection systems are also active in the case of a rollover and trigger corresponding protection devices, for example, airbags in the head region and additional seatbelt pretensioners. A rollover takes place more slowly than a head-on impact or side impact. The protection devices are therefore generally activated later than the start of the vehicle deceleration which leads to an impact. The autarchy time period for rollover protection is therefore, for example, 1 sec.
Capacitors, which are charged to a higher voltage than the battery, if appropriate using voltage boosters or step-up voltage converters, are generally used as energy reserves or energy storage devices for the emergency power supply. Such energy storage devices for maintaining the power supply of the vehicle occupant protection system using the respective expedient autarchy time are costly both in terms of space and time.
It is accordingly an object of the invention to provide an emergency power supply system and a method for controlling the emergency power supply of at least two loads which overcome the above-mentioned disadvantages of the prior art apparatus and methods of this general type.
In particular, the invention is based on the object of reducing the expenditure necessary for the emergency power supply.
If during the autarchy time period the energy storage device has applied power to the power load assigned to it in order to carry out a function, the energy storage device is generally not completely discharged but rather, owing to the voltage demand of the power load, still contains a residual energy owing to ohmic line resistances, etc. This energy can be used to supply power to the other power load. If no discharge has taken place via the assigned power load, a large proportion of the stored energy is generally available at the end of the autarchy time period.
The predetermined conditions that lead to using the residual energy can be of different types. They may consist in a decision being made very early that the assigned power load is not required, that it has been activated, or simply that the autarchy time has expired.
The inventive method can be used for any emergency power supply systems in which, similarly to the vehicle occupancy protection system, power loads are supplied with different autarchy time periods and/or different voltage requirements by energy storage devices that are used for the emergency power supply. It goes without saying that the power load that is supplied with the residual energy of the energy storage device assigned to another power load generally has a longer autarchy time period and lower voltage requirements than the power load that is supplied by the energy storage device whose residual energy is used. However, power loads with higher voltage requirements can also be supplied with residual energy via suitable voltage converters.
As a result of using the available residual energy, the energy storage device or storage devices which is/are additionally supplied can be made smaller. Furthermore, less energy has to be stored for the emergency power supply.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for controlling an emergency power supply of at least two power loads. The method includes steps of: assigning an energy storage device of the power supply to one of the at least two power loads; after a failure of a power source for a predetermined autarchy time period, using the energy storage device to ensure that power is supplied to the one of the at least two power loads; and after an occurrence of at least one predetermined condition, using residual energy present in the energy storage device to supply power to another one of the at least two power loads.
In accordance with an added mode of the invention, a firing device of a vehicle occupant protection system is provided as one of the at least two power loads, and a power load of the vehicle occupant protection system is provided as one of the at least two power loads.
With the foregoing and other objects in view there is provided, in accordance with the invention, an emergency power supply system for a vehicle occupant protection system, that includes: at least one control unit; a firing device associated with an autarchy time period; a first energy storage device for supplying energy to the control unit; a second energy storage device for supplying energy to the firing device; and an energy source for supplying energy to the first energy storage device and to the second energy storage device. When the energy source fails, the first energy storage device and the second energy storage device supply energy to the control unit and to the firing device during predetermined autarchy time periods. The control unit is associated with an autarchy time period that is longer than the autarchy time period associated with the firing device. The emergency power supply system also includes a controllable switch for connecting the second energy storage device to the first energy storage device so that residual energy available in the second energy storage device is available for supplying power to the control unit.
In accordance with an added feature of the invention, the switch is controlled to close after an expiration of the autarchy time period associated with the firing device.
In accordance with an additional feature of the invention, the switch is controlled to close after the firing device is fired.
In accordance with another feature of the invention, the control unit controls the switch and the firing device.
In accordance with a further feature of the invention, the firing device is configured for triggering a first safety device in an event of a head-on impact; and the control unit is configured to control a triggering of a second safety device in an event of a rollover.
In accordance with a further added feature of the invention, the firing device includes a firing cap and two electronic switches connected in series with the firing cap; and the switches are switched to a conductive state in order to fire the firing cap.
In accordance with a further additional feature of the invention, there is provided, a voltage booster having an output connected to the second energy storage device. A third energy storage device provides energy to the control unit. The third energy storage device is connected downstream of the energy source. A voltage reducer has an input connected to the output of the voltage booster. The voltage reducer has an output connected to the third energy storage device.
In accordance with yet an added feature of the invention, the second energy storage device is connected to the switch via the voltage reducer and the voltage booster.
In accordance with yet an additional feature of the invention, there is provided, a voltage booster having an output connected to the second energy storage device; and voltage reducer having an input connected to the output of the voltage booster. The voltage reducer has an output connected to the second energy storage device. The voltage booster has an input connected to the second energy storage device by the switch.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for controlling the emergency power supply and the emergency power supply system, in particular for a vehicle occupant protection system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.